Improving the quality of service for voice over internet protocol (VoIP) over wireless Local Area Networks (LANs) is on the critical path to achieving the vision of the unwired enterprise. Achieving high quality VoIP poses several challenges, particularly in heavily loaded systems. Wireless systems generally use signal strength as the determinant factor for which wireless access point should accept a communication session with a mobile device. In many situations, a small number of access points become overloaded as those access points are in high usage areas but have the best signal strength.
As a calling party or mobile user moves relative to an access point, the RF bandwidth requirements may change (increase or decrease) drastically, depending on the change in distance. Since this change is not accounted for by traditional call admission control algorithms, resource overload can result. Counting sessions as they arrive, for instance, and denying calls beyond a specific number requires over-engineering to account for bandwidth variability. RF-based connections, unlike wired connections, are subject to much more interference (i.e., other radios, noise sources, etc.), which can affect RF bandwidth requirements for the session. RF bandwidth is partitioned across different traffic classes, voice, video, and data, which may result in unused RF bandwidth, if not needed by one of the traffic classes. As callers move from one access point zone to the next access point zone, the likelihood of the adjacent access point taking over the call must remain high (almost independent of call volume) to prevent unexpected disconnections.
Presently, there are no good methods for balancing load based on other factors beyond signal strength and addressing the other issues mentioned above. Direct measurement of RF utilization is generally not available. Hybrid techniques for estimating RF utilization by applying mathematical models to partial measurements are relatively complex, particularly from modeling the behavior in the collision region, and therefore impractical. Further, user datagram protocol (UDP) traffic is not separately balanced for load. Finally, load balancing is generally accomplished only when bandwidth is completely allocated, which can cause errors when trying to quickly move loads to other systems.